1. Field of the Invention
This invention relates to a television camera, and more particularly to a television camera using a high refractive index glass material of 1.6 or higher as the prism of color resolution optics.
2. Description of the Prior Art
In a color TV camera, a color resolving prism system is disposed behind an objective lens so as to resolve an image forming beam into three color component lights and image the lights on the surfaces of three to image pickup tubes corresponding to the respective color components. Each of the image pickup tubes scans the image pickup surfaces and converts a picture into an electrical signal.
Image pickup tubes using a fluorescent material such as PbO, AsSes, CdSe or the like as the image pickup surface are common and in a TV camera employing these, it is effective to always impart uniform light of low illumination, namely, the so-called bias illumination to the image pickup surfaces in order to enhance the rising response speed and afterimage characteristic of the image pickup tubes, and the color resolution optics usually has this bias illumination device.
Various color resolving prisms have heretofore been proposed. Typical color resolving prisms are those disclosed in U.S. Pat. No. 3,202,039, German Open Patent Publication No. 2,063,049 and U.S. Pat. No. 3,798,354. A bias light device is known from U.S. Pat. No. 3,767,846.
The configuration of the conventional prism system and the bias illumination method have been developed for the glass material of the prism system such as BK7 or the like which has a refractive index of about 1.5.
Recently, however, to meet the requirements of the optical system for compactness, light weight and high performance, the use of a prism system called a high index prism using a high refractive index glass material of about 1.6 or higher refractive index has been studied, but where a high refractive index glass material is used for the conventionally configured color resolving prism, the critical angle becomes smaller and accordingly this resutls in shading of the bias light.